The present invention relates to in situ extraction of carbonaceous values from oil shale and other carbonaceous deposits and pertains particularly to the extraction of carbonaceous values from surface and near surface formations.
It is well known that enormous deposits of subterranean carbonaceous deposits exist throughout the world today. Such deposits exist in the form of coal, oil shale, and tar sands, for example.
Commercial development of oil shale has lagged in this country because it has been unable to compete with other sources of petroleum. Several proposals for the recovery of carbonaceous values have been made in the past. These proposals have one or more drawbacks which prevent them from being economically feasible.
In situ retorting is one proposal that continues to be of interest today for deep subsurface deposits. Several approaches to in situ retorting have been proposed for such deposits. These approaches are generally exemplified by the following U.S. patents and the prior art cited therein: U.S. Pat. No. 1,913,395 issued June 13, 1933; U.S. Pat. No. 1,919,636 issued July 25, 1933; U.S. Pat. No. 2,481,051 issued Sept. 6, 1949; and U.S. Pat. No. 3,661,423 issued May 9, 1972.
These approaches involve breaking up the subterranean formation into rubble, and retorting the rubble. These processes require that a portion of the deposit be removed by mining, solution, drilling, or some other method in order to provide a free face for breakage, and to create space for bulking of the rock broken by the explosive.
Surface and near surface formations of carbonaceous deposits such as oil shale are normally mined by conventional mining methods and the materials shipped to a retorting plant built for the extraction of carbonaceous values from such materials. The plant may be located at the site of the mining operation or some distance away. After the values have been extracted from the shale, the waste products must be transported from the plant and disposed of in a suitable manner. Such an operation can become quite expensive because of the numerous handling steps within the process. Such an operation may also have ecological drawbacks unless the spent shale is deposited back in the formation and the earth restored to its original contour and surface condition.